var w = 800, h = 600;
var popW = 720, popH = 550;

if (document.all || document.layers) {
  w = screen.Width;
  h = screen.Height;
}
var leftPos = (w-popW)/2, topPos = (h-popH)/2;

function openForm(pG) {
  framesWindow = window.open(pG, 'formwin', 'width=' + popW + ',height=' + popH + ',top=' + topPos + ',left=' + leftPos + 'toolbar=no,status=no,scrollbars=1,dependent,resizable=no');
}